Heating assembly and method of production thereof



Feb. 24, 1959 w; H. NORTON 2,875,312

HEATING ASSEMBLY AND METHOD OF PRODUCTION THEREOF Filed Sept. 27, 1956 2 Sheets-Sheet 1 5 42; J9] a5 10/ f4 JUL E1722]? /%'//m/2/ A Warn Z Feb. 24, 1959 w. O O 2,875,312

HEATING ASSEMBLY AND METHOD OF PRODUCTION THEREOF Filed Sept. 27, 1956 2 Sheets-Sheet 2 15725.27 ZLUF United States Patent HEATING ASSEMBLY AND METHOD OF PRODUCTION THEREOF William H. Norton, Chicago, lll., assignor to Thermel, Inc., Franklin Park, Ill., a corporation of Delaware Application September 27, 1956, Serial No. 612,390

3 Claims. (Cl. 219-19) This invention relates to a heating device, and more particularly, to an electrical heating unit adapted for cooking or similar heating operations.

In general, there are two types of cooking units employed. One type, known as the surface type, involves the use of a heating element mounted on a base of an open refractory support. This type of unit has interest and popularity with the development of refractory thermally conductive and electrically insulative cement, but almost invariably this unit leaves something to be desired particularly because of the tendency for the heating element to separate from the cement because of their differences in thermal expansion.

The other type of unit is known as the metal sheath" unit wherein the heating element is encased in and insulated from a sheet of metal. Such units have enjoyed considerable popularity because of their comparatively high efliciency and their speed of operation. Also, these units are employed industrially as a heating sheath for a pipe or similar conduit carrying material to be heated. The units may also be employed in flat platen form. These units have certain drawbacks, however, in that they are expensive to manufacture and they have a tendency to warp under usage. Both of these difficulties are caused to a substantial extent by the problem of providing a suitable electrically insulative mounting for the resistor or electrical heating element.

The instant invention provides an improved and simplified mounting arrangement for the resistor in a metal sheath unit. The assembling expense is materially reduced in the instant invention by the provision of sleevelike units which retain the resistor therein in an extremely sturdy mounting and which may be bent or otherwise shaped as desired to conform with the ultimate shape of the metal sheath. One important aspect of the instant invention resides in the compacting of the particulate mounting material which is used to maintain the resistor and the sleeve in closely spaced relationship; and such compacting is effected by filling the sleeve (with the resistor therein) with suitable particulate refractory material and then swaging the sleeve to increase the length thereof and reduce the diameter thereof. Such sleeves are then mounted on the back of a suitable retainer and, when desired, are formed while in firm assembly with the retainer into the ultimate shape desired for the heating device.

It is, therefore, an important object of the instant invention to provide an improved electric heater, and method of producing the same.

Another object-of the instant invention is to provide an improved electric heater member that is durable, sturdy, well protected and is capable of prolonged operatron.

A further object of the instant invention is to provide an improved electric heater comprising an elongated resistor, an electrically and thermally conductive sleeve closely surrounding the resistor, electrically insulative refractory particulate material filling the sleeve and mainice taining the resistor therein in closed spaced relation to the sleeve, said particulate material being compacted by swaging the filled sleeve to elongate the same at least 10%, and an electrically and thermally conductive retainer having a heating surface and a back side opposed thereto retaining the sleeve in firm assembly on the back side thereof.

Yet another object of the instant invention is to provide an improved method of preparing an electric heater that comprises mounting an elongated resistor within an electrically and thermally conductive sleeve, filling the sleeve with electrically insulative refractory particulate material and swaging said sleeve by the application of impact and high pressure forces around the outer periphery thereof to lengthen the sleeve by at least 10% While maintaining the resistor spaced from the inner periphery of the sleeve, whereby the particulate material is compacted.

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.

On the drawings:

Figure l is a side elevational view, with parts broken away and parts shown in section, of a sleeve unit employed in the preparation of the heating device of the instant invention; v

Figure 2 is an elevational view, comparable to Figure 1, showing the sleeve unit of Figure 1 after it has been swaged to the size desired;

Figure 3 is an elevational sectional view of a retainer employed in the practice of the instant invention for mounting the sleeve of Figure 2;

Figure 4 is a sectional elevational view showing the retainer of Figure 3 mounting the sleeve of Figure 2 in assembled form;

Figure 5 is a sectional elevational view, comparable to Figure 4, but showing an assembly providing a different retainer structure;

Figure 6 is a sectional elevational view, comparable to Figure 3, showing a different retainer structure;

Figure 7 is a sectional elevational view comparable to Figure 4 showing the sleeve of Figure 2 mounted in the retainer of Figure 6;

Figure 8 is a sectional elevational view comparable to Figures 4 and 7 showing still a different structure for the assembled retainer and sleeve;

Figure 9 is a top plan view of a sheath unit embodying the instant invention, comprising the retainer and sleeve assembly of Figure 4;

Figure 10 is a sectional detail view taken substantially along the line X-X of Figure 9;

Figure 11 is a fragmentary top plan view showing the connecting means and structure for a sheath unit made from the assembly of Figure 5; and

Figure 12 is a sectional elevational view comparable to Figure 5 showing a different structural arrangement for the assembly.

As shown on the drawings:

In Figure 1, the reference numeral 10 indicates generally a sleeve unit employed as a starting assembly in the fabrication of an electric heater embodying the instant invention. The sleeve unit 10 comprises an elongated helical resistor 11 (made of Nichrome or similar heating element wire), an electrically and thermally conductive sleeve 12 (made of stainless steel) closely surrounding the resistor 11, and electrically insulative refractory particulate material (magnesia) 13 filling the sleeve 12 and maintaining the resistor 11 therein in closely spaced relation to the sleeve 12. The opposite ends 11:: and 11b of the resistor 11 are carried in the electrically insulative plugs 14a and 14b, respectively, which also serve to close off the ends of the sleeve 12.

In assembling the sleeve, unit 19, the resistor 11 is mounted within the sleeve 12 and in a plug 14a fitted at one end of the sleeve 12. The plugs 14a and 14b are preferably made of hard rubber or any insulative packing material. Electrical grade magnesia particles are then fed into the open end of the tube 12, while vibrating the tube 12 to compact the magnesia 13 as much as possible, until the magnesia 13 fills the tube 12. The plug 14b is then mounted to close the tube 12 and to maintain the resistor terminal 11b insulated from the sleeve 12.

The next step in the practice of the instant invention involves the swaging of the sleeve unit so as to obtain a sleeve unit 10', shown in Figure 2, wherein the diameter D of the unit 16 has been reduced from 10 to about 40% to obtain the diameter D of the swaged unit 10'. Also, the length of l of unit 19 has been increased at least 10% (and preferably from 10 to 40%) so as to obtain the length l for the unit 19. The swaging is accomplished by the application of impact and high pressure forces around the outer periphery of the unit 10. It is important to retain the substantially circular cross-section of the unit 10 in the swaged unit 10' (even though the diameter D is reduced), so the impact and pressure forces are employed around the entire outer periphery and, of course, for the full length of the unit 10. In carrying out the swaging, the unit 10 is placed between mating metal dies having mating semi-cylindrical grooves therein of substantially the size and shape of the swaged unit 10, and the original unit it) is subjected to hammering between these dies.

The eifect of the swaging is to compact the particulate material 13 to its unit density, or substantially so. In other words, the magnesia 13 is compacted to sub stantially the density of magnesia per se. In fact, it is not until substantially this density is reached that reduction in the Wall thickness of the tube 12 is obtained. This results in elongation to obtain the tube 12' in the unit 1%, which is longer and has thinner walls as well as a reduced diameter D. For the sake of convenience the resistor 11 is shown as a single line in Figures 1 and 2, and the resistor 11 remains substantially unchanged in helix diameter during the swaging operation. The walls of the tube 12 are moved only slightly closer to the resistor 11 in the finally swaged unit 10 and this reduction in spacing is effected during the actual compacting of the magnesia particles 13, rather than during the metal working which results in the reduction of the wall thickness and the elongation of the tube 12. The extent of this reduction in spacing can be readily ascertained and the helix diameter of the resistor 11 and the tube diameter D may be computed accordingly. The important feature here is that swaging is carried out to an extent suihcient to actually work the metal to reduce the wall thickness and elongate the tube 12. Swaging to this extent accomplishes maximum compacting. In addition, swaging around the entire periphery of the tube 12' affords uniform reduction in diameter D and uniform centering or spacing of the concentrically aligned resistor helix 11, As will be appreciated, the individual loops of the resistor helix 11 must be spaced from each other and, more important, they must be spaced from the inside walls of the tube 12 in order to avoid shorting out the heater.

The next step in the practice of the instant invention involved providing an electrically and thermally conductive retainer 20 (Figure 3) having a heating surface 29a and a back side 20b opposed thereto and retaining means in the form of a groove 21 defined by closely spaced ridges 22 and 23. As will be noted from Figure 3 retaining means for a second sleeve unit (not shown) are also provided in the form of a second groove 24 defined by closely spaced ridges 25 and 26. The retainer 20 is preferably formed by extrusion and it may be made of aluminum, copper or some other conveniently extrudable metal. Most preferably, it is made out of aluminum or copper. In the extrusion of the retainer 20, the heating surface 20a is formed as smoothly as possible, since a smooth heating surface 20a has been found to be important (particularly for conduction heating through surface-to-surface contact with an object, 1 not shown, to be heated).

. length to receive the entire sleeve unit 10, or a plurality thereof in a plurality of grooves 21, 24.

As indicated in Figure 4, wherein the sleeve units indicated at 10' and 10" are shown in cross-section, the

retainer is altered in shape. This results from the assembly operation which involves first placing sleeve units 10 and 10 in grooves 21 and 24 of theextruded retainer element 20, followed by bending the ridges over to obtain retaining ridges 22 and 23' holding the unit 10' in firm assembly and ridges and 26 holding a the unit 10" in firm assembly. It will be noted that the grooves 21' and 24' are matingly formed to fit the sleeve units 10' and 10" for surface-to-surface contact throughout at least about 180 of the periphery of each of the units 10' and 10", and preferably at least about 270 7 of the periphery of each. This affords a maximum amount of surface-to-surface contact so that the greater portion of the heat generated within the unit 10 will flow by conduction into the aluminum body of the retainer 20' and then out across the heating surface 20a.

, Referring now to Figure 5, which shows a plurality of swaged sleeve units 10, 10", 10", all of which have the same structure as the swaged unit 10' shown in Figure 2, it will be seen that these units ltl, etc. are mounted in a retainer structure 30 differing from the retainer structure 29-29 shown in Figures 3 and 4. In the retainer structure 30, retaining means are provided in the form of grooves 31, 32, 33 matingly receiving the swaged sleeve units 10', 10", 10" and defined by closely spaced ridges 34, 35, 36 and 37. Again, the retainer 30 is preferably extruded aluminum. In the assembly of Figure 5, however, a backing member indicated generally by the reference numeral 38 is provided for closing the mouths of the grooves 31, 32, 33 to retain the sleeves 10, etc. in firm assembly therein. The backing member 38 comprises a matingly grooved backing strip 39, 40, 41 for each of the grooves 31, 32, 33. Each backing strip 39, etc. is in close fitting (sliding) relation to the immediately adjacent ridges 34, 35 so as to obtain surfacet-o-surface contact therebetween, and the strip 39 is matingly grooved to obtain surface-to-surface contact with the back of the swaged sleeve unit 10. The same is true for the strips 40 and 41. The backing strips 39, 40, 41 are preferably also made of extruded aluminum (or the same material that the retainer 30 is made of) and the positioning of these strips 39, 40, 41 is such as to effect surface-to-surface contact between a highly conductive (aluminum) retainer body (composed of the retainer 30 and the strips 39, etc.) throughout the entire periphery of each unit 10. This assures maximum heat conductivity from the unit 10 through the strip 39 and the retainer body 30 to a heating surface 30a on the retainer 30.

The backing member 38 is also formed of a backing band 42 urged against the back of each of the strips 39, 40, 41 and generally along the top of the ridges 34, 35, 36, 37. The backing band 42 is preferably made of a less conductive metal than that of the retainer 30 and strips 39, etc. Conductivity of heatis desired in the direction of the heating surface 30a. For this reason the backing band 42 is preferably made of stainless steel, which is of finn assembly in the unit of Figure 5.

Referring now to Figure 6, it will be seen that an extruded aluminum retainer 50 is shown provided with retaining means in the form of elongated passages 51 and 52 of the size of the swaged sleeve The elongated passages are provided generally on the back side 5012 of the retainer 50 which is opposed to the heating surface 500. In using the retainer 50, swaged units 10' and 10", again identical in structure to the unit 10' of Figure 2, are forced into the passages 51 and 52 so as to obtain surface-to-surface contact substantially throughout the entire periphery of each of the swaged units 10' and 10". Such surface-to-surface contact may be improved by a secondary swaging or hammering operation performed on the retainer 50 after the units 10' and 10" have been inserted in the passages 51 and 52. In general, the assemblies of Figures 4 and 7 are relatively simple in structure and easily fabricated. The assembly of Figure 5, however, has the advantage that individual swaged units 10', etc. may be replaced without any difficulty or without substantial destruction of the assembly, merely by loosening the backing band 42 and removing a unit 10 with the backing strip 39, in order to replace the unit 10.

As shown in Figure 8, a retainer 60 (shown only partially) has a substantially rectangular cross-section with a plurality of circular elongated passageways, only two of which 61 and 62 are shown, formed therein opposite a heating surface 60a. Actually the retainer 60 is twice the width here shown having two additional passageways (not shown) which repeat the pattern of the structure shown in the passageways 61 and 62. As shown, a swaged unit 10 is snugly fit in the passageway 61 and a hollow tube of copper 63 or other suitable metallic conductor is snugly fit in the passageway 62. The retainer 60 may be extruded with the empty passages 61 and 62 formed therein, so that these passages 61 and 62 may be subsequently filled by the unit 10 and the hollow tube 63; or the retainer 60 may be extruded over the unit 10 and the hollow tube 63 (preferably using a stainless steel tube in this case) so as to provide a portion of the retainer 60 opposite the heating surface 60a with a sleeve unit 10' and a hollow tube 63 embedded therein. This results in excellent surface-to-surface contact, because the extruded retainer 60 will cool and shrink slightly after the extrusion process. It will also be appreciated that the assembly of Figure 7 may be formed by extruding the retainer 50 over the units 10' and 10" (as mandrels in the extrusion process) in the same manner as that just described for the retainer 60.

The retainer 60 is equipped with a plurality of heating units 10', etc., only one of which is here shown, so that the retainer 60 can function in substantially the same manner as the previously described retainers for heating purposes. In addition, the retainer 60 is provided with alternately positioned hollow tubes 63, etc., only one of which is shown, so that rapid cooling can be effected. It will further be appreciated that a cooling tube such as the tube 63 can be mounted in the manner described in connection with the retainer 60 in place of any of the heating units in each of the various other retainers described herein, although this specific embodiment is shown here only in connection with the retainer 60. The particular function of the cooling tube 63 is the rapid cooling of the retainer 60 and the material heated thereby. This is particularly useful, for example, in plastic injection molding machines, wherein a heating band formed from, for example, the retainer 60 is wrapped around the nozzle or feed portion of the molding machine whereat the plastic is fed into the dies, in order to maintain a desired high temperature at this location. The desired high temperature retains the necessary fluidity in the plastic material at this critical location; but many plastic materials tend to deteriorate quite rapidly if held at the high temperature employed at this specific location. Accordingly, whenever a machine is to be shut down temporarily, it is very diflicult to prevent deterioration of the plastic material that happens to be at this criticat location. The instant device 60 permits extremely rapid cooling, so that the deterioration of the plastic can be avoided.

Any suitable cooling fluid may be controllably connected to the tube 63, so that the cooling fluid can be forced therethrough at the desired time, for example, when the electric current is taken off the heating tube 10. It will also be appreciated that the tube 63 in the embodiment of Figure 8 could be eliminated, because the passageway 62 is a closed passageway. In embodiments such as Figures 4 and 5, however, a tube would be necessary to retain the cooling fluid.

Referring now to Figure 9, there is shown a heating unit indicated generally by the reference numeral which comprises a pair of allochiral semi-annular heating members 101 and 102 matingly mounted to define an annulus for receiving an article (not shown) to be heated. Such article may be a cooking pot which fits rather snugly in the annular heating device 100 and is supported thereby or it may be a section of a pipe conducting material to be heated. The shape of the cross-section Y-Y of the arcuate member 101 is shown in Figure 4, although it will be appreciated that the view shown of the arcuate member 101 would also permit it to have cross-sectional views such as those shown in Figures 7 and 8. The member 101 is formed by bending the sleeves 10' and 10 and retainer 20 as assembled (in Figure 4) into an arcuate shape (of substantially a uniform radius) with the heating surface 20a defining the inner periphery. Bending in this manner is of particular importance, because this forces the sleeves 10' and 10" to be urged more firmly into the grooves 21' and 24' for better surface-tosurface contact therebetween. In addition, during heating the retainer body 20 tends to expand and further urge the retainer 20 against the units 10' and 10" to improve the heat conductivity across contiguous faces thereof.

In order to complete the assembly 100, it will be noted that at one end 101a of one arcuate member and one end 102a of the other arcuate member 102, the sleeve units 10, 10", etc. are turned radially outwardly to provide clamping lugs, shown best in Figure 10, at A, B, C and D. A yoke member 103 is urged against the back side of the members A and B and a yoke member 104 is urged against the back side of the members C and D and a tie bolt 105 connects the yoke members 103 and 104 and mounts adjustable nuts 106 and 107 against which springs 108 and 109 are backed, respectively, so as to urge the yoke members 103 and 104, respectively, toward each other and thus resiliently urge the arcuate members 101 and 102 together. The same mounting is shown at the left-hand side of Figure 9. In this way superior surfaceto-surface contact may be maintained between the heating surface 28 and an article to be heated during expansion and contraction of the arcuate members 101 and 102.

A comparable mounting for the assembly of Figure 5 is shown in Figure 11. In this case, opposing equivalent elements are indicated by the same reference numeral primed. As will be seen the heating surfaces 30a and 30a form the inner periphery. Opposed sleeve units 10' and 10"" are connected to bar contacts 110 and 111 con nected to a suitable source of electrical energy (not shown) and the ends of the stainless steel backing bands 42 and 42' are turned radially outwardly to define flange members 112 and 113 which receive a tie bolt 114 with lock nuts 115 and 116 at the extremities thereof each backing a spring 117 and 118, respectively, urging the flange portions 112 and 113, respectively, toward each other. This also affords compensation for expansion and contraction during heating and cooling, so that superior surface-to-surface contact may be maintained between the heating surfaces 30a and 30a and an article (not shown) to be heated. Also, it will be appreciated that the stainless steel backing bands 42 and 42 assist materially in urging the units 10' and 10" into surface to-surface contact With the retainers 3t? and 30'.

Referring now to Figure 12, it will be seen that a retainer 70 is shown which compares withthe retainer 30 of Figure 5, except that the backing member 38 of Figure 5 is composed of separable units whereas only a backing band 82 is used in conjunction with the retainer 70. The retainer 70 mounts a plurality of swaged sleeve units 10, 10, 10", all of which have the same structure as the swaged unit 10 shown in Figure 2, In the retainer 70, retaining means are provided in the form of grooves 71, 72 and 73 matingly receiving the swaged sleeve units 10, 10" and 10' and defined by closely spaced ridges 74, 75, 76 and 77. Again, the retainer 70 is preferably extruded aluminum. In the assembly of Figure 12, as in the assembly of Figure 5, a backing strip 8?. is provided for closing the mouths of the grooves 71, 72, 73 to retain the sleeves 10, 1.0", 10' in firm assembly therein. As mentioned, however, backing strips such as the strips 39, 40 and 41 are not employed in the assembly of Figure 5 and, instead, the backing strip 82 directly engages the sleeves 10', 10", 10. The backing strip 82 (which is preferably formed of stainless steel) thus firmly urges the sleeves 10', 1t), 10' against the bottoms of the grooves 71, 72, 73 so as to obtain best heat conductivity through the retainer 70. in order to assure contact between the backing member 82 and the sleeves 10', 1t)", 10 the grooves 71, 72, 73 are formed shallow enough, or the ridges 74, 75, 76 and 77 are short enough so as not to contact the backing member 82. Actually, there is a very close toierance here to avoid appreciable heat losses through convection, but the contact is made between the backing strip 82 and the sieeves 16', etc. This provides a very simple and etlicient unit which can be readily assembled and disassembled. In addition, the stainless steel backing strip 82 has a lower coefficient of expansion than the aluminum retainer 70, so that heating up of the aluminum retainer '70 merely results in tighter surface contact between the sleeves 10', etc. and the retainer 70.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

I claim as my invention:

1. In an electric heater, in combination, an elongated resistor, an electrically and thermally conductive sleeve closely surrounding the resistor, electrically insulative refractoiy particulate material filling the sleeve and maintaining the resistor therein in closely spaced relation to the sleeve, said particulate material being compacted by swaging the filled sleeve to elongate the same at least 10%, an aluminum retainer having a heating surface and a back side opposed thereto, means on said back side defining an open-topped groove receiving said sleeve, and a stainless steel backing band covering the open-topped groove and retaining the sleeve therein in firm assembly, said retainer, sleeve and backing band being bent into an arcuate shape with the heating surface on the concave side and the backing band on the convex side of the arc.

2. A heater as claimed in claim 1 wherein the backing band directly engages said sleeve.

' 3. A heater as claimed in claim 1 wherein a matingly grooved backing strip is interposed between and in direct Contact with the backing band and said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,359,400 Lightfoot NOV. 16, 1920 1,614,938 Wiegand Jan. 18, 1927 1,731,120 Abbott Oct. 8, 1929 1,869,140 Gelinas July 26, 1932 1,911,063 Daly May 23, 1933 2,499,961 Lennox Mar. 7, 1950 2,677,122 Oakley May 4, 1954 2,701,410 Huck et al. Feb. 8, 1955 2,722,591 Fry Nov. 1, 1955 2,747,070 Bargehr May 22, 1956 2,777,043 Duray et al. Jan. 8, 1957 2,786,125 Drugmand et a1 Mar. 19, 1957 2,802,086 Fener Aug. 6, 1957 FOREIGN PATENTS 720,939 Great Britain Dec. 29, 1954 

